1. Field of the Invention
This invention relates to an optical apparatus having visual axis detecting means, and particularly to an optical apparatus having visual axis detecting means for detecting the axis in the direction of a target point being observed by an observer (photographer) through a finder system on an observation surface (focusing screen) on which an object image by a photographing system is formed, i.e., the so-called sight axis (visual axis), by the utilization of the reflected image of the observer's eyeball obtained when the surface of the observer's eyeball is illuminated, and effecting various photographing operations.
2. Related Background Art
There have heretofore been proposed various apparatuses (for example, eye cameras) for detecting what position on the observation surface an observer is observing, i.e., detecting the so-called sight axis (visual axis).
For example, in Japanese Laid-Open Patent Application No. 1-274736, a parallel light beam from a light source is projected onto the front eye part of an observer's eyeball and the sight axis is found by the utilization of the corneal reflected image by reflected light from the cornea and the imaged position of the pupil.
FIG. 10 of the accompanying drawings illustrates the principle of a visual axis detecting method.
FIG. 1A of the accompanying drawings shows an eyeball image in a very usual case where it is projected onto the surface of the image sensor 14 of FIG. 10, and the numeral 60 in FIG. 1B of the accompanying drawings designates an image signal output on a line (I)--(I)'.
In FIG. 1A, the numeral 50 represents the so-called white of the eyeball, the numeral 51 represents the pupil, and the numerals 52a and 52b represent the corneal reflected images of an eyeball illuminating light source.
FIG. 2 of the accompanying drawings shows an example of the eyeball image of a photographer wearing spectacles. The numerals 52a and 52b represent corneal reflected images, and the numerals 53a, 53b, 54a and 54b represent the ghost images of the light source by the spectacle.
The visual axis detecting method will now be described with reference to FIG. 10 and FIGS. 1A and 1B. Infrared light emitting diodes 13a and 13b are disposed substantially symmetrically in Z direction with respect to the optical axis ax.sub.1 of a light receiving lens 12, and divergently illuminate the photographer's eyeball.
Infrared light emitted from the infrared light emitting diode 13b illuminates the cornea 16 of the eyeball 15. At this time, the corneal reflected image d by part of the infrared light reflected by the surface of the cornea 16 is condensed by the light receiving lens 12 and is re-imaged at a position d' on an image sensor 14.
Likewise, infrared light emitted from the infrared light emitting diode 13a illuminates the cornea 16 of the eyeball. At this time, the corneal reflected image e by part of the infrared light reflected by the surface of the cornea 16 is condensed by the light receiving lens 12 and is re-imaged at a position e' on the image sensor 14.
Light beams from the end portions a and b of an iris 17 form the images of the end portions a and b on the image sensor 14 through the light receiving lens 12. If the rotation angle .theta. of the optical axis ax.sub.2 of the eyeball 15 relative to the optical axis ax.sub.1 of the light receiving lens 12 is small, when the Z coordinates of the end portions a and b of the iris 17 are Za and Zb, the coordinates Zc of the central position c of the pupil 19 are expressed as EQU Zc.perspectiveto.(Za+Zb)/2.
Also, the Z coordinates of the middle point of corneal reflected images d' and e' and the Z coordinates Zo of the center of curvature O of the cornea 16 coincide with each other and therefore, when the Z coordinates of positions d' and e' at which the corneal reflected images are created are Zd and Ze and the standard distance from the center of curvature O of the cornea 16 to the center C of the pupil 19 is L.sub.OC and a coefficient which takes the individual difference relative to the distance L.sub.OC into account is A1, the rotation angle .theta. of the optical axis ax.sub.2 of the eyeball substantially satisfies the following relational expression: EQU (A1.times.L.sub.OC).times.sin .theta..perspectiveto.Zc-(Zd+Ze)/2(1)
Therefore, in a visual axis calculation processing apparatus, by detecting the positions of respective characteristic points (corneal reflected images d, e and the end portions a and b of the iris) projected onto portions of the image sensor as shown in FIG. 1B, the rotation angle .theta. of the optical axis ax.sub.2 of the eyeball can be found. At this time, expression (1) is rewritten into EQU .beta.(A1.times.L.sub.OC).times.sin .theta..perspectiveto.(Za'+Zb')/2 -(Zd'+Ze')/2 (2)
where .beta. is a magnification determined by the position of the eyeball relative to the light receiving lens 12, and is substantially found as a function of the spacing .vertline.Zd'-Ze'.vertline. between the corneal reflected images. The rotation angle .theta. of the eyeball 15 is rewritten into EQU .theta..perspectiveto.ARCSIN{(Zc'-Zf')/.beta./(A1.times.L.sub.OC)}(3)
where EQU Zc'.perspectiveto.(Za'+Zb)/2 EQU Zf'.perspectiveto.(Zd'+Ze')/2.
Now, the sight axis does not coincide with the optical axis ax.sub.2 of the photographer's eyeball and therefore, when the rotation angle .theta. of the optical axis ax.sub.2 of the photographer's eyeball in the horizontal direction is calculated, the angle correction .delta. of the optical axis of the eyeball and the sight axis is effected, whereby the photographer's visual axis .theta.H in the horizontal direction can be found. When a coefficient which takes the individual difference relative to the correction angle .delta. of the optical axis ax.sub.2 of the eyeball and the sight axis into account is B1, the photographer's visual axis .theta.H in the horizontal direction is found as EQU .theta.H=.theta..+-.(B1.times..delta.) (4)
where as regards the signs .+-., when the rightward rotation angle with respect to the photographer is positive, if the photographer's eye looking into the observation apparatus is the left eye, the sign + is selected, and if the photographer's eye looking into the observation apparatus is the right eye, the sign "-" is selected.
Also, in FIG. 10, there is shown an example in which the photographer's eyeball rotates in Z-X plane (for example, a horizontal plane), but detection is likewise possible when the photographer's eyeball rotates in X-Y plane (for example, a vertical plane). However, the component of the photographer's visual axis in the vertical direction coincides with the component .theta.' of the optical axis of the visual axis in the vertical direction and therefore, the visual axis .theta.V in the vertical direction is EQU .theta.V=.theta.'.
Further, from visual axis data .theta.H and .theta.V, the positions (Zn, Yn) on the focusing screen in the finder field the photographer is seeing are found as EQU Zn.perspectiveto.m.times..theta.H .perspectiveto.m.times.[ARCSIN{Zc'-Zf')/.beta./(A1.times.L.sub.OC)}.+-.(B1 .times..delta.)] (5) EQU Yn.perspectiveto.m.times..theta.V,
where m is a constant determined by the finder optical system of the camera.
The values of coefficients A1 and B1 for correcting the individual difference of the photographer's eyeball can be found by making the photographer fixate at a target disposed at a predetermined location in the finder of the camera, and making the location of the target and the position of the fixation point calculated in accordance with expression (5) coincident with each other.
The calculations for finding the photographer's visual axis and fixation point in the present embodiment are executed by the software of the microcomputer of the visual axis calculation processing apparatus on the basis of the aforementioned express ions.
The coefficients for correcting the individual difference of the visual axis are found, the position, on the focusing screen, of the visual axis of the observer looking into the finder of the camera is calculated by the use of expression (5), and the visual axis information is utilized for the focus adjustment of the photo-taking lens or for exposure control or the like.
As described above, the direction coordinates of the photographer's visual axis can be calculated from the positional relation between the corneal reflected image ("Purkinje's image", hereinafter referred to as "P-image") of the infrared light emitting diode for illumination (hereinafter referred to as "IRED") and the pupil in the eyeball image. A specific detection system for this is disclosed in U.S. patent appln. Ser. No. 07/888,495 (filed on May 27, 1992).
Since the P-image is the corneal reflected image of the IRED, its luminance is high in the whole of the eyeball image, and since that image is also the reflected image of the chip light emitting surface of the IRED, its size is very small. Accordingly, if those characteristics are utilized, the P-image can be extracted from the eyeball image signal. Specifically, where the luminance value of a certain pixel in the eyeball image signal exceeds a predetermined value and the luminance difference between that pixel and the pixels around it exceeds a predetermined level, that pixel (or the surrounding pixel area including that pixel) is chosen as the candidate for the P-image.
Further, design is made such that one set of two IREDs is turned on to detect the distance between the camera and the eyeball and the P-image is used in a pair and therefore, when there are a plurality of objects for the pair of P-images, a pair of P-images having an appropriate spacing therebetween is selected.
When as shown in FIGS. 1A and 1B, there are one set of high luminance portions (52a and 52b), it can be readily detected with the aforedescribed condition that these high luminance portions are right P-images.
However, when as shown in FIG. 2, there are a plurality of sets of high luminance portions, it will often be the case with the aforedescribed condition alone that the P-images are erroneously selected, and this is very inconvenient for visual axis detection.